1. Field of the Invention
The present invention relates to a semiconductor package, and more particularly, to a semiconductor package with a high reliability and fabrication method thereof.
2. Description of the Related Art
Recently, as a variety of electronic devices are miniaturized, the circuits for driving these electronic devices are also highly integrated. In other words, circuits and electronic parts are integrated in a single semiconductor package and mounted on printed circuit board (PCB).
As an example of the semiconductor package, there is a ball grid array (hereafter, referred to as BGA) package in which a plurality of ceramic substrates each having a plurality of circuit patterns are stacked, the substrates are electrically connected to each other through via holes and solder balls are attached to electrode pads.
FIG. 1 illustrates a process of manufacturing a general ball grid array package. FIG. 2 is a flowchart illustrating a process of manufacturing the general ball grid array package shown in FIG. 1.
Referring to FIGS. 1 and 2, the fabrication of the BGA package starts with cutting a green tape wound on a roller 12 in a predetermined size (S21). Here, the green tape is formed as follows. Glass powder, bonding agent for maintaining viscosity of the glass powder, plasticizer for providing the bonding agent with flexibility so as to prevent the bonding agent from hardening, solvent for dissolving the bonding agent and the plasticizer, and small amounts of additional agents are mixed and dried to form slurry. The dried slurry is processed using a tape casting technique to be wound on the roller 12. Necessary substrates are provided by cutting the wound green tape in a predetermined size.
A plurality of via holes 16 are formed using a mechanical punching technique on four green tapes 13a-13d provided at the step S21 (S22).
Subsequently, a conductive paste 18 is filled in the via hole 16 and the filled conductive paste 18 is dried (S23). Here, the dried conductive paste serves as electrode pads.
The conductive paste 18 filled in the via hole 16 connects circuit patterns 20 formed on the green tapes 13a-13d with each other electrically during a post process.
After the conductive paste is filled in the via hole 16 at the step S23, the circuit patterns 20 are formed on the green tapes 13a-13d by using a screen printing technique (S24).
A solder resist is coated on the lowest green tape 13d on which the electrode pad 54 is formed among the green tapes 13a-3d on which the circuit patterns 20 are formed at the step S24 (S25). Here, the solder resist is coated on the entire surface of the lowest green tape 13d except the electrode pad 54.
The remaining green tapes 13a-13c are aligned on the lowest green tape 13d coated with a solder resist at the step S25 (S26).
If the four green tapes 13a-13d are aligned at the step S26, the four green tapes 13a-13d are stacked and adhered to each other at a laminating process (S27).
The green tapes 13a-13d adhered to each other at the step S27 are co-fired with a predetermined heat (S28). Each of the green tapes 13a-13d co-fired at the step S28 acts as a ceramic substrate and the ceramic substrates stacked at the step S28 becomes a circuit package 15 having a plurality of circuit layers.
Electronic components 2 including passive elements such as resisters R, inductors L, capacitors C and active elements such as transistors and integrated circuit chip (IC) are mounted on the package 15 provided at the step S28 (S29).
A material 5 functioning as a passivation layer is coated on the entire surface of the package 6 on which the electronic components are mounted (S30).
Lastly, each of solder balls 3 is adhered to each of the electrode pads positioned on the lower surface of the coated package 9 by using a solder ball reflow process (S31).
When the BGA packages 10 manufactured as described above are mounted on a printed circuit board (PCB) or another substrate, the solder ball of the BGA package is adhered to the electrode pad formed on the PCB or the electrode pad formed on the substrate.
Alternatively, if necessary, the BGA package 10 may be formed by adding a process of coating an electrode pad on the substrate after firing the stacked substrate.
Generally, the solder resist 1 formed on the BGA package 10 is formed using a screen printing technique on the area which the electrode pads do not exist.
However, in the laminating process in which a predetermined heat and pressure are used and in a firing process, nonuniform coating area and thickness of the solder resist cause the electrode pad to react with a firing substrate and thus damage the electrode. The solder ball 3 adhered to the electrode pad by a nonuniform solder resist is adhered in nonuniform shape, which deteriorates the reliability of the BGA package.
As shown in FIG. 3, since the solder resist 1 coated on the lowest green tape 13d slopes slightly, the shape of the solder ball 3 adhered to the edge of the solder resist 1 also slopes slightly.
The solder ball 3 is easily deformed by the external force 52, as the height of the solder ball 3 decreases. In other words, as the height of the solder ball 3 increases, the solder ball 3 is not easily deformed by the external force. This is because the cohesion of the solder ball 3 increases. The deformation of the solder ball deteriorates the reliability of the BGA package.
Furthermore, green tapes 13a-13g used as a substrate and the solder resist 1 coated on the green tape shrink physicochemically in a firing process. Then, if the shrinkage of the solder resist 1 is different from that of the green tapes 13a-13g, the BGA package in the firing process is cracked and deformed. To this end, it is necessary to develop a solder resist having the same shrinkage as that of the green tape.
Accordingly, in the conventional BGA package manufacturing method, the BGA package is cracked and deformed since the solder resist made of the material different from that of the substrate and the shrinkage of the substrate is different from that of the solder resist.
Additionally, in the conventional BGA package manufacturing method, the electrode pad. is reacted with a firing substrate and the electrode pad is injured due to nonuniform coating area and nonuniform coating thickness of the solder resist.
Furthermore, in the conventional BGA package manufacturing method, since cohesion of the solder ball adhered to the electrode pad is decreased due to the solder resist coated on the substrate, the shape of the solder ball is deformed and the solder ball is adhered nonuniformly to deteriorate the reliability of the BGA package.